(BE-58,,59): extend db schema & build stock transfer api

- Extend DB schema for stock transfers
- Build stock transfer API (create,)

internal/database/migrations/20251014024702_create_stock_transfer_delivery_items.up.sql

@@ -0,0 +1,35 @@
+-- ===============================================================
+--  STOCK TRANSFER DELIVERY ITEMS (PIVOT)
+-- ===============================================================
+
+CREATE TABLE IF NOT EXISTS stock_transfer_delivery_items (
+    id BIGSERIAL PRIMARY KEY,
+    stock_transfer_delivery_id BIGINT NOT NULL,
+    stock_transfer_detail_id BIGINT NOT NULL,
+    quantity NUMERIC(15, 3) NOT NULL CHECK (quantity > 0)
+);
+
+-- FOREIGN KEYS
+DO $$
+BEGIN
+    IF EXISTS (SELECT 1 FROM pg_tables WHERE tablename = 'stock_transfer_deliveries') THEN
+        ALTER TABLE stock_transfer_delivery_items
+            ADD CONSTRAINT fk_delivery_items_delivery
+            FOREIGN KEY (stock_transfer_delivery_id)
+            REFERENCES stock_transfer_deliveries(id)
+            ON DELETE CASCADE ON UPDATE CASCADE;
+    END IF;
+
+    IF EXISTS (SELECT 1 FROM pg_tables WHERE tablename = 'stock_transfer_details') THEN
+        ALTER TABLE stock_transfer_delivery_items
+            ADD CONSTRAINT fk_delivery_items_detail
+            FOREIGN KEY (stock_transfer_detail_id)
+            REFERENCES stock_transfer_details(id)
+            ON DELETE CASCADE ON UPDATE CASCADE;
+    END IF;
+END $$;
+
+-- INDEXES
+CREATE INDEX IF NOT EXISTS idx_stock_transfer_delivery_items_delivery_id ON stock_transfer_delivery_items (stock_transfer_delivery_id);
+
+CREATE INDEX IF NOT EXISTS idx_stock_transfer_delivery_items_detail_id ON stock_transfer_delivery_items (stock_transfer_detail_id);